System and method for dynamic bandwidth allocation on PONs

ABSTRACT

Mechanisms for providing a subscriber-side interface with a passive optical network are described herein. An optical network termination (ONT) having an integrated broadband passive optical network processor is utilized to receive downstream data from an optical line termination (OLT) via a passive optical network and provide the contents of the downstream data to one or more subscriber devices via one or more data interfaces. Similarly, the ONT is adapted to receive and transmit upstream data from the one or more subscriber devices to the OLT via the passive optical network. The ONT preferably implements one or burst buffers for buffering upstream and/or downstream data. The ONT can be adapted to notify the OLT of the status of the burst buffer, thereby allowing the OLT to modify the bandwidth allocations.

FIELD OF THE INVENTION

The present invention relates generally to communication using broadbandpassive optical networks and more particularly to buffering data inpassive optical networks.

BACKGROUND OF THE INVENTION

A number of network technologies have been developed for connecting theso-called “last mile” between a central office and subscriber. One suchdevelopment is the passive optical network (PON). PONs typically includea fiber optic network between a central office (CO) and a subscribercomprising active network devices only at the CO and at the subscriberpremises. As such, PONs generally require less power to operate, aremore reliant, and can be upgraded without having to upgrade the plantbetween the CO and the subscriber.

PONs often are used to provide multiple types of data content, such asvoice, data, and video, over the same network. To properly distributethis content, a number of common network protocols, such as Ethernet andAsynchronous Transfer Mode (ATM), are used to deliver the content overthe PON. ATM PONs, or APONs, are particularly well suited for deliveringreal-time content, such as voice or videoconferencing, due to Quality ofService (QoS), small cell size, and other features incorporated by theATM protocol. A specification for APONs has been adopted by theInternational Telecommunication Union (ITU) as Recommendations G.983.1,G.983.2, G.983.3, G.983.4, and G.983.5 (collectively known herein as theITU G.983.X Recommendation). These recommendations address APON systemswith symmetrical line rates of 155.520 Mbps and asymmetrical line ratesof 155.520 Mbps upstream and 622.080 Mbps downstream. Therecommendations also cover the physical layer requirements andspecifications for the physical media dependent layer for an APON rangeup to 20 km (12.4 miles), the trans-convergence (TC) layer, security,and a ranging protocol. Additionally, dynamic bandwidth allocation (DBA)and data protection mechanisms are outlined.

Referring now to FIG. 1, an exemplary implementation of a known PON isillustrated. The known system 100 includes a central office 104 havingan optical line termination (OLT) 110 connected to a number of opticalnetwork terminations (ONTs) 130-134 via a PON 120. Data, video, and/orvoice content from various content providers is delivered to the OLT 110of the CO 104. The OLT 110 typically is a component of an accessmultiplexer shelf that terminates the optical network in the CO 104. Itreceives and transmits APON optical signals via a fiber management shelfutilized to route between access multiplexer shelves and the outsidefiber plant (PON 120). An optical module of the OLT 110 performs opticalfiltering, electronic-to-optical (E/O) conversion, andoptical-to-electrical (O/E) conversion. The upstream data (i.e., fromthe subscriber devices to a content provider via the OLT 110) isde-framed, OAM extracted, and upstream data multiplexed with otherupstream data before being sent to a back plane bus interface, such as aUtopia Optical Connection Level 3 (OC3) physical interface. The backplane upstream bus interface, by means of a vendor specific method(dedicated pipe, shared structure with share/grant mechanisms, etc.)sends the data to the network interface connected to the one or morecontent servers.

Conversely, downstream data (i.e., from the content server to thesubscriber devices via the OLT 110 and an ONT) is routed to the OLT 110by means of a vendor specific interface method (dedicated pipe, sharedstructure with share/grant mechanisms, etc.) from the networktermination through the back plane bus interface to the APON interfaceof the OLT 110 (such as by a Utopia OC3 or OC Layer 12 (OC 12) physicalinterface). The downstream data is placed into the appropriate data slotassigned to the intended ONT of the ONTs 130-134. OAM is added to thedata, the data is framed, and then sent to the optical transmitter ofthe OLT 110. This ATM downstream data is encrypted by the APON interfaceutilizing a key received from each ONT 130-134 specifically for eachONT's own data stream. In addition to the data interfacing function, theback plane bus may contain a separate management interface for equipmentinventory & management, facilities management of ONT services, permanentvirtual circuit (PVC) assignment, virtual circuit (VC)/virtual path (VP)cross connection management, alarm surveillance, etc.

The ONTs 130-134 are the components that terminate the optical link ofthe PON 120 at the customer premises. For example, the ONT 130terminates outside of the subscriber premises 150, where the ONT 130 canbe used to: provide voice content (e.g., VoIP) to/from one or moretelephones 152 via a RJ11 twisted pair line; provide network data (suchas Internet content) to one or more computers 154 over an Ethernetnetwork; and provide video (either analog or digital) to one or moretelevisions 156. The ONTs 130-134 typically include an optical modulethat performs optical filtering, E/O conversion, O/E conversion, anddownstream clock recovery. Downstream data received from the OLT 110 isde-framed, OAM extracted, and processed according to its content and/ordestination (voice, network data, video) by the APON interface 140. Forexample, downstream voice content is provided to a telephone 152 (oneexample of a subscriber device) via a voice interface 142, downstreamvideo content is provided to a video display 156 (another example of asubscriber device) via a video interface 146, and data content, such asdata from a server on the Internet, is provided to a computer 154 (yetanother example of a subscriber device) via the data interface 144.Upstream data from subscriber devices intended for the CO 104 iscollected from the interfaces 142-146, multiplexed into a data stream,framed, and OAM inserted before being sent to an optical transmitter ofthe ONT 130. The transmitter data is adjusted into its proper systemtime slot by the APON interface 140 by offsetting its transmit dataclock (by an amount determined by the ranging protocol) relative to thedownstream clock.

While the use of optical network terminations (ONTs), also known asnetwork interface devices (NIDs) or optical network units (ONUs), inpassive optical networks provides a great deal of flexibility in datacontent, data transmission rates, and other design considerations, knownONTs have a number of limitations. For one, known ONTs typicallyimplement the functionality of the APON interface 140 and the subscriberinterfaces 142-146 as discrete devices often connected via a printedcircuit board. However, the implementation of separate devices for theAPON interface 140 and the subscriber interface 142-146 exhibitsnumerous disadvantages. For one, the use of separate devices on a PCBlimits the reduction of the size of the ONT. Additionally, utilizingseparate devices to provide PON processing functionality results inunnecessarily high power consumption, as the interfaces between thedevices results in power loss due to parasitic capacitance, currentleak, poorly controlled interfaces between the devices, and the like.Likewise, the signal loops on the PCB and the interconnects produce arelatively large amount of electromagnetic interference (EMI) which caninterfere with the operation of the ONT. Similarly, the connectionsbetween devices and PCBs and the traces between the devices of the PCBoften are somewhat unreliable, so by implementing a relatively largenumber of devices to provide PON processing functionality, thereliability of the ONT can be compromised. Another limitation isresource duplication between the devices, since each device oftenimplements some common functionalities, such as memory, memory accesscontrollers, registers, and the like. Additionally, by using numerousdiscrete components to implement the PON processing capability of theONT, ONT manufacturers often must keep large inventories of theindividual devices on hand.

In addition to the limitations of the physical structure of known ONTs,PON standards, such as the ITU G.983.X Recommendation, are deficient ina number of areas. For example, the ITU G.983.X Recommendation providesfor a rudimentary data protection method referred to “churning.”However, the churning key used in accordance with the G.983.XRecommendation is only 24 bits long, a key length that is recognized bythose skilled in the art as relatively weak. Additionally, although theG.983.X Recommendation makes provision for the dynamic allocation ofbandwidth between the OLT and the ONTs, it is incumbent on the OLT toanalyze the data transfer status between the OLT and the ONTs in orderto modify the bandwidth allocations.

In view of the limitations of known optical network terminationimplementations, improved mechanisms for providing passive opticalnetwork connectivity to subscribers would be advantageous.

SUMMARY OF THE INVENTION

The disclosed technique mitigates or solves the above-identifiedlimitations in known implementations, as well as other unspecifieddeficiencies in the known implementations.

In an optical network termination in optical communication with anoptical line termination via a passive optical network and operablycoupled to at least one subscriber device, a burst buffer is provided inaccordance with one embodiment of the present invention. The burstbuffer comprises an upstream buffer portion adapted to buffer upstreamdata from the at least one subscriber device and means for providing arepresentation of a status of the upstream buffer portion to the opticalline termination for use in dynamic bandwidth allocation by the opticalline termination.

In an optical network termination in optical communication with anoptical line termination via a passive optical network and in electricalcommunication with at least one subscriber device, a burst buffer isprovided in accordance with one embodiment of the present invention. Theburst buffer comprises a downstream buffer portion adapted to bufferdownstream data from the optical line termination and means forproviding a representation of a status of the downstream buffer portionto the optical line termination for use in dynamic bandwidth allocation.

In accordance with another embodiment of the present invention, anoptical network termination in optical communication with an opticalline termination and in electrical communication with at least onesubscriber device is provided. The optical network termination comprisesa burst buffer including a downstream buffer portion adapted to bufferdownstream cells from the optical line termination and an upstreambuffer portion adapted to buffer upstream cells from the at least onesubscriber device. The optical network termination further comprises adeframer in electrical communication with the burst buffer and beingadapted to identify a subset of downstream cells from a bitstreamtransmitted from the optical line termination to the optical networktermination, the bitstream being representative of downstream data fromthe optical line termination and provide the subset of downstream cellsto the burst buffer for buffering. The optical network termination alsocomprises an overhead insertion module in electrical communication withthe burst buffer and being adapted to extract the upstream cellsbuffered in the burst buffer and insert overhead into each of theextracted upstream cells.

In accordance with an additional embodiment of the present invention, apassive optical network is provided. The passive optical networkcomprises an optical line termination, at least one subscriber device,and at least one optical network termination in optical communicationwith the optical line termination and operably coupled to the at leastone subscriber device. The optical network termination includes a burstbuffer having an upstream buffer portion adapted to buffer upstream datafrom the at least one subscriber device and a downstream buffer portionadapted to buffer downstream data from the optical line termination. Theoptical network termination further includes means for providing arepresentation of a status of the burst buffer to optical linetermination. The optical line termination is adapted to dynamicallyallocate a portion of a bandwidth of the passive optical network to theoptical network termination based at least in part on the status of theburst buffer.

In an optical network termination in optical communication with anoptical line termination via a passive optical network and in electricalcommunication with at least one subscriber device, a method is providedin accordance with one embodiment of the present invention. The methodcomprises the steps of storing upstream data from the at least onesubscriber device in an upstream buffer portion of a burst buffer,storing downstream data from the optical line termination in adownstream buffer portion of the burst buffer, and providing arepresentation of a status of the burst buffer to the optical linetermination.

In an optical network termination in optical communication with anoptical line termination via a passive optical network and in electricalcommunication with at least one subscriber device, a computer readablemedium is provided. The computer readable medium comprises a set ofinstructions being adapted to manipulate a processor to store upstreamdata from the at least one subscriber device in an upstream bufferportion of a burst buffer, store downstream data from the optical linetermination in a downstream buffer portion of the burst buffer, andprovide a representation of a status of the burst buffer to the opticalline termination.

In an optical line termination in optical communication with an opticalnetwork termination via a passive optical network, a method is providedin accordance with yet another embodiment of the present invention. Themethod comprises the steps of receiving, from the optical networktermination, a representation of a fullness of an upstream bufferportion of a burst buffer of the optical network termination, theupstream buffer portion being adapted to buffer upstream data from atleast one subscriber device and receiving, from the optical networktermination, a representation of a fullness of a downstream bufferportion of the burst buffer, the downstream buffer portion being adaptedto buffer downstream data from the optical line termination. The methodfurther comprises the steps of allocating a portion of an upstreambandwidth of the passive optical network to the optical networktermination for upstream transmission of the upstream data based atleast in part on the fullness of the upstream buffer portion andallocating a portion of a downstream bandwidth of the passive opticalnetwork to the optical network termination for downstream transmissionof the downstream data based at least in part on the fullness of thedownstream buffer portion.

In an optical line termination in optical communication with an opticalnetwork termination via a passive optical network, a method is providedin accordance with one embodiment of the present invention. The methodcomprises the steps of receiving, from the optical network termination,a representation of a fullness of a first sub-buffer of a burst bufferof the optical network termination, the first sub-buffer beingassociated with a first upstream data content of upstream data from atleast one subscriber device and receiving, from the optical networktermination, a representation of a fullness of a second sub-buffer ofthe burst buffer, the second sub-buffer being associated with a seconddata content of the upstream data. The method further comprises thesteps of allocating a first upstream bandwidth portion to the opticalnetwork termination for upstream transmission of the first data contentof the upstream data based at least in part on the fullness of the firstsub-buffer and allocating a second upstream bandwidth portion to theoptical network termination for upstream transmission of the second datacontent of the upstream data based at least in part on the fullness ofthe second sub-buffer.

In an optical line termination in optical communication with an opticalnetwork termination via a passive optical network, a method is providedin accordance with one embodiment of the present invention. The methodcomprises the steps of receiving, from the optical network termination,a representation of a fullness of a first sub-buffer of a burst bufferof the optical network termination, the first sub-buffer beingassociated with a first downstream data content of downstream data fromthe optical line termination and receiving, from the optical networktermination, a representation of a fullness of a second sub-buffer ofthe burst buffer, the second sub-buffer being associated with a seconddata content of the downstream data. The method further comprises thesteps of allocating a first downstream bandwidth portion to the opticalnetwork termination for downstream transmission of the first datacontent of the downstream data based at least in part on the fullness ofthe first sub-buffer and allocating a second downstream bandwidthportion to the optical network termination for downstream transmissionof the second data content of the downstream data based at least in parton the fullness of the second sub-buffer.

Various embodiments of the present invention provide an integratedPON/Voice/Communications processor in accordance with the ITU G.983.XRecommendation. The implementation methods and level of integration canbe chosen to minimize cost and optimize performance of a broadbandpassive optical network termination (ONT) device. One objective of thepresent invention is to reduce the development cost of an ONT. Anotherobjective includes reducing net power consumption for the aggregatefunctionality required for broadband voice, video, and data service. Yetanother objective is to provide a scaleable and flexible PON opticsinterface capable of multiple symmetric/asymmetric configurations. Anadditional objective of the present invention is to provide scaleableupstream and downstream burst buffering to allow real time bandwidthcontrol/allocation (minimize cell loss ratio versus load, delay versussystem load) across the PON. The present invention finds particularbeneficial implementation in the FTTB (Fiber to the Business) and FTTH(Fiber to the Home) markets.

In at least one embodiment of the present invention, the functionalityof PON processing, ATM processing, video processing (e.g., digitalcable), voice processing (e.g., VoATM or VoIP), and data network (e.g.,Ethernet) processing is integrated onto into a single integratedcircuit, thereby providing an integrated device that can be used tointerface between a subscriber and an optical network. A subscriberplain old telephone system (POTS) service (one or multiple lines),private branch exchange (PBX) service, or an international publicswitched telephone network (ISPTN) service can be provided by on-chipvoice processing which is capable of providing voice coding, echocancellation, tone detection, tone generation, and fax. The customerdata service is provided via a data interface, such as a 10/100 Base-Tinterface or through an MII interface connected to another PHY devicesuch as an IEEE 802.11b interface, a Home Phoneline Network Alliance(HPNA) compliant interface, and the like. ATM processing provides forswitching and Layer 2,3 functionality required between the subscriberdevices and data network. PON processing provides for the physical layerframing, OAM, messaging, dynamic bandwidth allocation, and decryption ofdata toward the consumer.

By integrating the described functionality onto a single chip, thefollowing advantages may be realized: lower ONT power consumption asinterfaces between multiple processors can be better controlled; memoryresource sharing among multiple processors reduces power consumption,reduces resource duplication and reduces total system cost; lowerelectromagnetic interference (EMI) levels as signal loop areas arereduced since fewer high signal level interfaces and interconnects arerequired; higher reliability as fewer components and less PCB area arerequired; improved system diagnostics capability as functions such asself tests and loop backs can be easily included and controlled; and ONTsuppliers can stock less overall component inventory per ONT.

Still further features and advantages of the present invention areidentified in the ensuing description, with reference to the drawingsidentified below.

BRIEF DESCRIPTION OF THE DRAWINGS

The purposes and advantages of the present invention will be apparent tothose of ordinary skill in the art from the following detaileddescription in conjunction with the appended drawings in which likereference characters are used to indicate like elements, and in which:

FIG. 1 is a schematic diagram illustrating a known passive opticalnetwork implementation.

FIG. 2 is a schematic diagram illustrating an exemplary implementationof an ONT having an integrated PON processor in accordance with at leastone embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating another exemplaryimplementation of an ONT in accordance with at least one embodiment ofthe present invention.

FIG. 4 is a schematic diagram illustrating an exemplary implementationof an APON interface of an ONT in accordance with at least oneembodiment of the present invention.

FIG. 5 is a schematic diagram illustrating an exemplary implementationof an optical interface of the APON interface of FIG. 4 in accordancewith at least one embodiment of the present invention.

FIGS. 6A and 6B are schematic diagrams illustrating an exemplaryimplementation of a burst buffer of the APON interface of FIG. 4 inaccordance with at least one embodiment of the present invention.

FIG. 7 is schematic diagram illustrating an exemplary implementation ofa security module for providing data protection in the APON interface ofFIG. 4 in accordance with at least one embodiment of the presentinvention.

FIG. 8 is a schematic diagram illustrating an exemplary controller forcontrolling an operation of the APON interface of FIG. 4 in accordancewith at least one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the interest of brevity, a number of acronyms, initialisms, andabbreviations may be used in the following discussion. To provide auseful reference, these terms and their corresponding representation arelisted below:

ADSL Asymmetric Digital Subscriber Line APON ATM Over Passive OpticalNetwork ATM Asynchronous Transfer Mode BER Bit Error Rate BFP Back FacetPhotodiode BIP Byte Interleaved Parity BM LDR Burst Mode Laser DriverPON Broadband Over Passive Optical Network CATV Coaxial Cable TelevisionCLEC Competitive Local Exchange Carrier CO Central Office CM AGCContinuous Mode Automatic Gain Control CM CDR Continuous Mode Clock &Data Recovery CM TIA Continuous Mode Trans-Impedance Amplifier CRCCyclic Redundancy Check DBA Dynamic Bandwidth Allocation DFB DistributedFeedback Laser DS Downstream DSL Digital Subscriber Line DWDM DenseWavelength Division Multiplexing EMI Electro-Magnetic Interference EMSElement Management System E/O Electrical to Optical EPB ExtendedPeripheral Bus EPON Ethernet Over Passive Optical Network FEC ForwardError Correction FP-LD Fabry-Perot Laser Diode FSAN Full Service AccessNetwork FTTB Fiber to the Business FTTC Fiber to the Cabinet FTTH Fiberto the Home GPIO General Purpose Input/Output HEC Header Error ControlIEEE Institute of Electrical and Electronics Engineers ILEC IncumbentLocal Exchange Carrier ITU International Telecommunications Union IPInternet Protocol LAN Local Area Network LCD Loss of Cell DelineationLCP Local Convergence Point LCF Laser Control Field LD Laser Diode LSBLeast Significant Bit LT Line Terminal LVDS Low Voltage DifferentialSignaling MAC Media Access Control MAN Metropolitan Access Network MIIMedia Independent Interface MPEG 2 Motion Picture Experts Group-Layer 2MSB Most Significant Bit MSO Cable Multiple-System Operator NAP NetworkAccess Point NRZ Non Return to Zero NT Network Termination O/E Opticalto Electrical Conversion OAM Operations, Administration and MaintenanceOAN Optical Access Network ODF Optical Distribution Frame ODN OpticalDistribution Network OLT Optical Line Termination ONT Optical NetworkTermination ONU Optical Network Unit P2P Point to Point P2MP Point toMulti-Point PCB Printed Circuit Board PHY Physical Layer PLOAM PhysicalLayer Operations, Administration and Maintenance PON Passive OpticalUnit POP Point of Presence POTS Plain Old Telephone Service PRBSPseudo-Random Bit Sequence PSTN Public Switched Telephone Network QoSQuality of Service RFI Radio Frequency Interference RT Remote TerminalRx Receiver RXCF Receiver Control Field SLA Service Level Agreement SLICSubscriber Line Interface Chip SONET Synchronous Optical Network TCTransmission Convergence TDM Time Division Multiplex Tx Transmitter UNIUser Network Interface US Upstream VC Virtual Channel VOATM Voice OverAsynchronous Transfer Mode VOD Video On Demand VOIP Voice Over InternetProtocol VP Virtual Path VPI Virtual Path Identifier VPN Virtual PrivateNetwork WAN Wide Area Network WDM Wavelength Division Multiplexing

FIGS. 2-8 illustrate mechanisms for providing a subscriber-sideinterface with a passive optical network. In at least one embodiment, anONT having an integrated PON processor is utilized to receive downstreamdata from an OLT via a passive optical network and provide the contentsof the downstream data to one or more subscriber devices one or moreinterfaces. Similarly, the ONT is adapted to receive and transmitupstream data from the one or more subscriber devices to the OLT via thepassive optical network. Additionally, the ONT can implement a burstbuffer for buffering upstream and/or downstream data. In one embodiment,the ONT is adapted to provide OLT notification of the burst buffer,thereby allowing the OLT to modify the bandwidth allocations.Additionally, in one embodiment, the ONT implements one or moreencryption/decryption mechanisms, such as the digital encryptionstandard (DES), Triple DES (3DES), and Advanced Encryption Standard(AES), to provide data protection in excess of, or in place of, datachurning provided for in the ITU G.983 recommendations. The ONT can beadapted to interface with any of a variety of PONs, such as, forexample, an ATM PON (APON) or an Ethernet PON (EPON). Further, the ONTcan be adapted to transmit and/or receive information using a variety ofnetwork protocols and protocol combinations. To illustrate, the ONTcould be adapted for transmission/reception of Voice over ATM (VoATM),Ethernet over ATM, video encapsulation, and the like. Likewise, the datatransmitted can include data of a variety of different formats, such asvoice data, video data, file data, and the like. For illustrativepurposes, an exemplary implementation of the PON processor 240 using anAPON interface for use in an APON is discussed below. However, thoseskilled in the art can implement, using the guidelines provided herein,alternate PON interfaces, such as an EPON interfaces to an EPON, withoutdeparting from the spirit or the scope of the present invention.

Referring now to FIG. 2, an exemplary ONT 210 having an integrated PONprocessor is illustrated in accordance with the present invention. ONTsin accordance with at least one embodiment of the present invention,such as ONT 210, utilize an integrated PON processor 240 having both PONinterfacing functionality and one or more subscriber device interfacesimplemented on a single integrated circuit or device, such as anapplication specific integrated circuit (ASIC), a microcontroller, aprogrammable logic device (PLD), and the like. The APON interface 250and data interfaces 242-248 of the PON processor 240 are exemplary andillustrate a logical segmentation of the functionality provided by thePON processor 240 and are not intended to imply a specific physicalseparation of components within the integrated circuit of the PONprocessor 240.

In the illustrated embodiments optical signals representative ofdownstream data are transmitted via a PON, such as PON 120 of FIG. 1, tothe optical connector 220, wherein the optical connector 220 serves as acoupling device to the optical fiber of the PON 120. The opticalconnector 220 provides the optical signals to the optical module 230,wherein a wavelength division multiplexing (WDM) module 232 filters theoptical signal and provides the filtered signal to anoptical-to-electrical (O/E) converter 236. The O/E converter 236converts the filtered optical signal into its digital equivalent andthen provides the digital data representative of the filtered signal tothe APON interface 250. The APON interface 250, in one embodiment,processes upstream and downstream data in accordance with one or more ofthe ITU G.983.X Recommendations. Such processes can include APONframing/deframing, OAM extraction/insertion & OAM messaging, andranging/upstream time slot synchronization. For downstream data, theAPON interface 250, in one embodiment, deframes the downstream data toidentify and extract asynchronous transfer mode (ATM) cells and physicallayer OAM (PLOAM) cells from the downstream data. The downstream ATMcells or their payloads then are provided to one or more of theinterfaces 242-248 for any additional processing and subsequent outputto one or more subscriber devices. The extracted PLOAM cells can be usedby the APON interface 250 for management and configuration purposes.

Any of a variety of data interfaces may be utilized in accordance withthe present invention. As illustrated in FIG. 2, in one embodiment, thedata interfaces that can be implemented by the integrated PON processorinclude a voice interface 242, a video interface 244, and network datainterfaces 246, 248. The voice interface 242, in one embodiment, isadapted to decode voice content data from the APON interface 250 andprovide the resulting electrical signal representative of the voicecontent to one or more telephony devices over a telephone network, suchas a POTS, a PBX, or an IPSTN. Additionally, the voice interface 242 canbe further adapted to provide one or more of the following: voicecoding, echo cancellation, tone detection and generation, and fax anddata functionality.

Network data content, such as data from a server on the Internet, isprovided to one or more network data interfaces 246, 248 depending onits destination. Data content at the network data interface isde-encapsulated and re-encapsulated by the network data interface, ifnecessary, to conform to the protocol used by a data network to whichthe network data interface is connected. After any necessarymanipulation, the data interface transfers the data content over thedata network to one or more subscriber devices, such as a personalcomputer or handheld device. The network data interfaces 246, 248 caninclude any of a variety of network data interfaces, such as an Ethernetinterface, a token ring interface, an ATM interface, an IEEE 802.11binterface, a Home Phoneline Network Alliance (HPNA) 2.0 interface, andthe like.

For example, in one embodiment, the network data interface 246 includesan Ethernet interface for sending and receiving data from one or morecomputers connected to the ONT 210 via an Ethernet network and thenetwork data interface 248 includes a HPNA 2.0 compliant interface. Inthis example, the APON interface 250 extracts ATM cells from thedownstream data that are intended for a subscriber device on theEthernet network and provides the ATM cells to the Ethernet interface(network data interface 246). The Ethernet interface thende-encapsulates the ATM cells to obtain their data payload and thenre-encapsulates the data payloads into Ethernet frames. The Ethernetinterface then transmits the Ethernet frames over the Ethernet networkto the subscriber device. Similarly, ATM cells intended for a homephoneline network connected to the HPNA interface (network datainterface 248) can be de-encapsulated and their payloads arere-encapsulated into HPNA-compliant frames and the frames then can betransmitted to the destination subscriber device on the home phonelinenetwork.

Video content provided to the video interface 244 from the APONinterface 240 is processed/converted as necessary and the results areprovided to one or more video displays on a video network connected tothe video interface 244. For example, the downstream data could includevideo content data from a videoconference. In this case, the downstreamvideo content from an OLT can be transmitted in digital form to the APONinterface 250, whereupon the APON interface 250 provides the videocontent data to the video interface 244. The video interface 244, inthis example, then converts the digital data representing the videocontent into an NTSC-compliant analog electrical signal representativeof the video content. The video interface 244 can be adapted toimplement one or more of the following: Motion Pictures Experts Group(MPEG) decoding; MPEG encoding; audio & video stream delaysynchronization; re-modulation to create multiple analog video channels;and the like. Additionally, in at least one embodiment, the videointerface 244 is adapted to support one or more digital video formats,such as High Definition Television (HDTV).

Conversely, upstream data from the customer is received at theinterfaces 242-248, manipulated as necessary, and then provided to theAPON interface 250. The APON interface 250 multiplexes the separatecontents together, as appropriate, and then provides the multiplexedupstream data the optical module 230 for transmission to the OLT via thePON. Data received at the voice interface 242, in one embodiment, isencoded and converted into upstream ATM cells, and the ATM cells areprovided to the APON interface 250 for upstream transmission.Alternatively, the APON interface 250 can be adapted to frame the datafrom the voice interface 242 into ATM cells and then provide the ATMcells to the optical module 230 for transmission to the OLT. Likewise,the video interface 244 could be adapted to support interactive videoand any input received via the video interface 244 from a video displaycan be encoded as necessary and provided to the APON interface 250.Data, in the form of frames, packets, cells, and the like, is receivedat the network data interfaces 246, 248 andde-encapsulated/re-encapsulated (as appropriate) into ATM cells that areprovided to the APON interface 250.

The APON interface 250, upon receipt of ATM cells from the interfaces242-248, processes the upstream ATM cells in accordance with one or moreof the ITU G.983.X Recommendations. This processing can includeinsertion of OAM, data payload scrambling, adding APON overhead bytes,framing, and the like. The upstream data is provided from the APONinterface 250 to the electrical-to-optical (E/O) converter 234, whereinthe upstream data is converted from an electrical signal to an opticalsignal. The WDM module 232 filters the optical signal and provides theoptical signal to the optical connector 220, wherein the optical signalrepresentative of the upstream data is transmitted over the PON to theupstream OLT (such as OLT 110 of FIG. 1).

Referring now to FIG. 3, an exemplary implementation of an ONT 310having an integrated PON processor 340 is illustrated in accordance withat least one embodiment of the present invention. In the illustratedembodiment, the ONT 310 includes an optical connector 220, an opticalmodule 230, an integrated PON processor 340, an alternate interface 362,and physical ports 366, 370-378. As discussed with reference to FIG. 2,the optical connector 220 is used to transmit optical signals from theoptical module 230 to an OLT via a PON, such as PON 120 of FIG. 1, andprovide optical signals transmitted by the OLT via the PON to theoptical module 230. The optical module 230 is adapted to convert theoptical signal into electronic signals and vice versa. The opticalmodule 230 also is adapted to provide clock signaling to the PON 340 andto the OLT. Additionally, in at least one embodiment, the optical module230 is adapted filter the portion of the optical signal representing anvideo content, convert this portion to an analog electrical videosignal, and provide the analog video signal to one or more televisionsconnected to the ONT 310 via a video port 366 (e.g., a coaxial cableconnector).

The PON processor 340 (analogous to PON processor 240) includes anintegrated circuit having an APON interface 250, a network protocolmodule 320, a voice processing module 330, memory 304 (SRAM, forexample), a coder/decoder (Codec)/SLIC module 334, an Ethernet interface350, and a Media Independent Interface 360. The voice processing module330, in one embodiment, includes a digital signal processor adapted forvoice processing having a program memory bus, data memory buses,arithmetic logic unit, accumulators (including a multiply accumulator),application specific hardware, on chip memory, and any requiredperipherals (DMA controller, timers, clock generator). The networkprotocol module 320, in one embodiment, a communications module adaptedto implement one or more network protocol stacks, such asTelecommunications Protocol/Internet Protocol (TCP/IP), and can includea 10/100 BaseT Ethernet MAC & PHY, MII, an EPB with direct memory access(DMA) support and a 32 bit interface, one or more ARM 9 protocol &network processors with the appropriate RAM caches, an synchronousdynamic random access memory (SDRAM) controller, a DMA controller, powercontrol logic for power saving & clock gating, General PurposeInputs/Outputs (GPIOs), a network timing recovery capability, shareddata cache, a quality-of-service (QOS) engine for cell pacing/trafficshaping hardware assist, and loop back port. The network protocol module320 can provide the functionality of, for example, a communicationsprocessor available under the tradename Helium 210-80 from GlobespanVirata, Inc. of Red Bank, N.J.

Downstream data and clock information from the optical module 230 isreceived by the APON interface 250, whereupon the data is deframed intodownstream ATM cells and downstream Physical Layer OAM (PLOAM) cells, asdefined by the ITU G.983.X Recommendation. The downstream ATM cells arethen dechurned, if appropriate, and provided to the network protocolmodule 320. The downstream PLOAM cells can be used by the APON interface250 to control its operation. For example, PLOAM cells can includeinformation used to: control the upstream transmission timing for ONTson a PON; perform ranging to determine the transmission delay and otherrelevant information; measure the quality of a transmission; request achurning key from the ONTs; miscellaneous control functions; and thelike.

At the network protocol module 320, the data payloads of the downstreamATM cells are processed by an appropriate network protocol stack andthen routed to one or more of the voice processing module 330, theEthernet interface 330, or the MII 360 based on the content type of theATM cells. Voice content can be routed to the voice processing module330 for decoding and conversion into an analog signal for transmissionto one or more telephone devices over one or more telephone networksconnected to telephony ports 370-376. The voice processing module 330,in one embodiment, is adapted to provide a variety of telephony-relatedfunctions, including tone generation and removal, tone detection,network echo cancellation, voice encoding/decoding/transcoding, fax/datacapabilities, and the like. Likewise, in at least one embodiment, thevoice processing module 330 is adapted to support VoIP. The telephonyports 370-376 can include any of a variety of telephony-compatiblephysical ports, and preferably include RJ-11 ports.

Data content, such as web page data from a HTTP server on the Internet,can be framed into Ethernet frames by the protocol stack of the networkprotocol module 320 and then routed to the Ethernet interface 350 foroutput to one or more subscriber devices via a data network connected tothe Ethernet port 378. The Ethernet interface 350 can include any of avariety of Ethernet interfaces, such as 10-BaseT, 10-Base5, and thelike, and preferably includes a 10/100 Base-T interface. The Ethernetport 378 can include any of a variety of Ethernet-compatible ports, suchas a RJ-45 port, a coaxial cable port, and the like. Although FIG. 3illustrates an exemplary embodiment wherein the network data interfaceof an integrated PON processor includes an Ethernet interface, othernetwork data interfaces, such as an ATM interface or a fiber distributeddata interface (FDDI), may be used without departing from the spirit orthe scope of the present invention.

Alternatively, network data content and other types of data contentincluded in the downstream data, such as digital video content, can berouted by the network protocol module 320 to the Media IndependentInterface (MII) 360. As will be understood by those skilled in the art,Media Independent Interfaces often are used to provide transparentconnectivity between the MAC layer of an Ethernet device and thephysical layer of the network medium used by the Ethernet device.Accordingly, the MII 360 can be used to transmit/receiveEthernet-compliant frames of data between the network protocol module320 and the alternate interface 362, which can include a physicalinterface for any of a variety of physical mediums, such as 10-BaseFX,an HPNA-compliant interface, an IEEE 802.11b interface, and the like.

Conversely, for upstream data provided from one or more subscriberdevices over networks connected to the ports 366, 370-378, the data isreceived via the corresponding port and provided to the network protocolmodule 320. Voice content from the telephony devices is received via oneor more of the telephony ports 370-376 as an analog signal that isconverted to digital data by the CODEC/SLIC 334. The digital datarepresenting the upstream voice content is then processed by the voiceprocessing module 330 and provided to the network protocol module 320,whereupon it is processed by the appropriate network protocol stack,such as by encapsulating VoIP packets into upstream ATM cells, and thevoice data is provided to the APON interface 250. Upstream data contentfrom one or more subscriber devices is received via the Ethernet port378 and provided to the Ethernet interface 350, whereupon the datacontent is de-encapsulated/re-encapsulated as necessary and thenprovided to the network protocol module 320 for processing into upstreamATM cells. The network protocol module 320 then provides the upstreamATM cells to the APON interface 250. Similarly, data content or othercontents can be received from one or more subscriber devices via thealternate interface 362, provided to the network protocol module 320 viathe MII 360 for encapsulation into ATM cells, which are then provided,to the APON interface 250.

The APON interface 250 scrambles and frames upstream ATM cells from thenetwork protocol module 320, includes upstream PLOAM cells asappropriate, and provides the framed upstream data to the optical module230 for transmission to an OLT over a PON to which the ONT 310 isconnected. The functionality of the APON interface 250 is illustrated ingreater detail with reference to FIG. 4.

A number of advantages can be obtained by integrating the functionalityof various components of the PON processor 340 as a single integratedcircuit. For one, ONT developers typically can implement more easily asingle IC that provides an integrated solution compared to the effortand cost involved in developing an ONT using discrete components for itsPON processor. Secondly, the cost of implementing an integrated solutioncan be much lower than with discrete components. To illustrate, the APONinterface 240, the voice processing module 330, and/or the networkprotocol module 320 are adapted to share a single memory 304, such asSDRAM, for temporary data storage. However, if the APON interface 250,the voice processing module 330, and/or the network protocol module 320were to be implemented as separate, discrete components, as in knownsolutions, either a separate memory (e.g., RAM) must be implemented foreach discrete component or a complex memory access/control mechanismmust be implemented to allow shared access to the memory by the discretecomponents. As a result, significant time and effort could be expendedby the APON interface 250 in buffering the data between separatecomponents. Instead, by sharing the same memory (e.g., burst buffer 416,FIG. 4), the transmission of data between the elements of the APONinterface 250 typically is considerably faster due the decrease in thetime of transmission of electronic signals between elements, thedecrease in the complexity of the data buffering process betweenelements, and the like.

Although FIGS. 2 and 3 illustrate exemplary embodiments of an integratedPON processor having a voice interface, a video interface, and one ormore network data interfaces, the present invention is not intended tobe limited in number, type, and/or combination of data interfaces. Forexample, an integrated PON processor in accordance with the presentinvention can include a signal data interface, such as a single voiceinterface or a single network data interface. Alternatively, theintegrated PON processor can include a plurality of data interfaces, ofthe same or different types, such as an integrated PON having threenetwork data interfaces or two network interfaces and two voiceinterfaces. Although a variety of data interfaces are illustratedherein, those skilled in the art can implement other types of datainterfaces, using the guidelines provided herein.

Referring now to FIG. 4, an exemplary functionality of the APONinterface 250 is illustrated in greater detail in accordance with atleast one embodiment of the present invention. In one embodiment, theAPON interface 250 is implemented as a finite state machine comprisingtwo components: a controller (controller 430) and an upstream/downstreamdata path (represented by modules 404-426). The data path processes theupstream and downstream data for transmission and reception. In oneembodiment, two types of cells are processed by the data path: ATM cellsand PLOAM cells. ATM cells contain the data content, signalinginformation, and Operations and Management (OAM) information, whilePLOAM cells are utilized to provide physical infrastructure information,as well as data grants, PLOAM grants, ranging grants, access codes fromthe OLT, and the like.

Downstream Data Path

Downstream data (i.e., data received from an OLT via a PON), in oneembodiment, is routed through the optical Rx interface 404, the deframermodule 412, and either the controller 430 (PLOAM cells) or to one of thesecurity modules 422, 424 (ATM cells). The data contents of the ATMcells are then provided to the ATM layer of one or more network protocolstacks implemented by the network protocol module 320 (FIG. 3) forfurther processing. The components of the downstream data path arediscussed below:

Optical Rx Interface 404

The optical Rx interface 404, in one embodiment, is adapted to receivedownstream data from the O/E converter 234 of the optical module 230(FIG. 2), where the downstream data is representative of an electricalconversion of the optical signal that represents downstream contentbeing transmitted from an OLT to the ONT 210 across a PON. The opticalRx interface 404, in one embodiment, provides the framed downstream datato the deframer module 412 as a serial bit stream. Alternatively, theframed downstream data can be provided to the deframer module 412 asparallel data stream. The optical Rx interface 404 can include any of avariety of interfaces suitable for receiving data from an opticalmodule. An exemplary implementation of the optical Rx interface 404 isdiscussed with reference to FIG. 5.

Deframer Module 412

The deframer module 412 interfaces with the optical Rx interface 404 toreceive the bit stream representing the frames of data sent from theOLT. The deframer module 412, in one embodiment, delineates the receivedbit stream at each cell slot boundary of the bit stream to identify thecells. The delineated cells are filtered based on the header contents ofthe cells. Downstream PLOAM cells are provided to the controller 430 forfurther processing. In at least one embodiment, the controller 430 usethe information contained in the PLOAM cells to control the operation ofthe APON interface 250, as noted above.

However, since the PON architecture is a single point-to-multipointnetwork architecture, data sent from an OLT over a PON typically isreceived by all OLTs connected to the PON unless extensive filtering orother relatively expensive or power consuming mechanisms are used.Accordingly, virtual path (VP) identifiers, as well as virtual circuitidentifiers, often are used to identify the source and intendeddestination of an ATM cell. Accordingly, in one embodiment, the deframermodule 412 is adapted to compare the virtual path (VP) identifiers ofdownstream ATM cells with the VP identifiers associated with the PONprocessor 240. Those downstream ATM cells having matched VP identifiersare passed to one of the security modules 422, 424 via the burst buffer416 for further processing. ATM cells with mismatched VP are discardedby the deframer module 412.

Burst Buffer 416

It will be appreciated that the data transfer rate between points of anetwork such as a PON often varies significantly, or is “bursty,”resulting in data being transmitted at a rate greater than the dataprocessing rate of the destination ONT, resulting in overflow.Alternatively, the data is transmitted at a rate less than the dataprocessing rate of the destination ONT, resulting in data starvation.Accordingly, in at least one embodiment, the APON interface 250implements a burst buffer 416 to buffer upstream and downstream data toprevent overflow and/or starvation. The burst buffer 416 can beimplemented using any of a variety of buffer architectures, such as RAM,registers, cache, flash memory, and the like. For example, the burstbuffer 416 can include embedded SRAM available under the tradenameIT-SRAM macro® available from MoSys, Inc. of Sunnyvale, Calif. The burstbuffer 416 preferably is implemented as part of the PON processor 340.However, in other embodiments, the burst buffer 416 can be implemented“off-chip”, such as in system memory. An exemplary implementation of theburst buffer 416 is illustrated with reference to FIG. 6.

In at least one embodiment, the overhead insertion module 414 insertsAPON overhead bytes after upstream ATM/PLOAM cells are retrieved fromthe burst buffer 416 for upstream transmission. As a result, thedownstream cells and the upstream cells are of the same size (e.g., 53bytes), thereby allowing the burst buffer 416 to be shared between theupstream and downstream data paths without requiring a complex controlmechanism that generally would be required if the upstream anddownstream cells were of different sizes. Additionally, because the cellsizes are the same, the burst buffer 416 can be allocated with lessdifficulty. Accordingly, should the properties of the upstream anddownstream data path change (i.e., the user uploads a large file), theallocation of the storage of the burst buffer 416 between the upstreamdata path and the downstream data path can be more easily adjusted andmanaged.

Security Modules 422, 424

Since downstream data from an OLT typically is received at everydownstream ONT on a certain PON in the absence of expensive protectionmechanisms, the ITU G.983.X Recommendation has implemented a rudimentarysecurity mechanism to protect downstream data from unauthorized access.This rudimentary security mechanism includes the process of “churning”(a form of encryption) the payloads of the downstream ATM cells at anOLT prior to transmission of the cells over the PON to the ONTs. Oncereceived at the intended ONT, the ONT “dechurns” the payloads of the ATMcells prior to providing the “clear” ATM cells to the ATM layer of anetwork protocol stack for further processing. Accordingly, in at leastone embodiment, the security modules 422, 424 are adapted to dechurnreceived ATM cells to generate clear ATM cells.

However, while the data can be churned per se prior to transmission tothe ONT, the ITU G.983.X Recommendation defines a churning key length of24 bits, a length that generally is considered insufficient for robustprotection. As such, in at least one embodiment, the payload data of thedownstream ATM cells are encrypted prior to transmission using a morerobust symmetric or asymmetric encryption scheme, such as the DataEncryption Standard (DES), Triple DES, Rivest, Shamir, & Adleman (RSA)encryption, and the like. Accordingly, the security modules 422, 424, inone embodiment, are adapted to decrypt the cell payloads using theappropriate decryption key in addition to, or rather than, dechurningthe payload using the churning/dechurning mechanism defined by the ITUG.983.X Recommendation. To illustrate, the ONT 210 could be used toreceive data from a data source using an OLT. Prior to transmitting therequested data, the data source could use a public key provided by theONT to encrypt the data before it is provided to the OLT. The OLT thencan chum the encrypted data and provide the churned and encrypted datato the ONT. The ONT then can dechurn the data to obtain the encrypteddata, which the ONT then can decrypt to obtain the “clear” data from thedata source. Instead of churning the already encrypted data, the OLT canbe adapted to provide the encrypted data from the data source to the ONTwithout unnecessarily churning the encrypted data.

In at least one embodiment, the OLT connected to the ONT 210 can beadapted to associate multiple APON identifiers with a single connectionwith the APON interface 250, where each APON identifier can beassociated with a different data content type, source, and/ordestination. For example, video data and voice data each could have adifferent APON identifier. Using these different APON identifiers, theOLT can be adapted to encrypt the video data with a different encryptionalgorithm or key than the encryption algorithm or key used to encryptthe voice data based in part on their different APON identifiers.

The use of different encryption schemes for different data sources canbe performed to provide an additional layer of security or it can beused to improve the efficiency of the encryption of data, as some typesof content may be less confidential than others or more easilyencrypted. Accordingly, in one embodiment, each of a plurality of APONidentifiers implemented by the PON processor 340 (FIG. 3) is associatedwith a different security module of the APON interface 250. In thiscase, the deframer module 412 can be adapted to route a downstream cellto one of the security modules 422, 424 based on its APON identifier. Inthis case, each of the security modules 422, 424 is adapted to implementa different decryption scheme/decryption key to decrypt the receivedcell payload data as appropriate.

In one embodiment, the security modules 422, 424 are implemented asseparate hardware components of an integrated PON processor 340. Forexample, the PON processor 340 could implement two separate circuits,each adapted to implement one of the two security modules 422, 424different encryption schemes. Alternatively, the PON processor 340 couldimplement the security modules 422, 424 as two instances of a singlesoftware function run on a single processor, each instance having adifferent decryption key and/or decryption algorithm. The cleardownstream ATM cells from the security modules 422, 424 are provided toan ATM layer of a network protocol stack (such as a protocol stackimplemented by the network protocol module 320 of FIG. 3) for furtherprocessing. One exemplary implementation of the security modules 422,424 utilizing a more robust encryption/decryption mechanism isillustrated in greater detail with reference to FIG. 7.

Upstream Data

Upstream data (i.e., data received by an ONT from one or more subscriberdevices), in one embodiment, is provided to the APON interface 250 inthe form of ATM cells from the ATM layer of a network protocol stack andprovided to the cell-type switch 420. Likewise, upstream PLOAM cellsgenerated by controller 430 are provided to the cell-type switch 420.Based on control signals from the controller 430, the cell-type switch420 selects from the PLOAM cell input and the ATM cell input to provideeither an ATM cell or a PLOAM cell to the scrambler 418. It will beappreciated that the ATM protocol describes the addition of a PLOAM cellto a frame at a certain interval (e.g., 5 microseconds) or after acertain number of ATM cells have been placed in a frame. Accordingly,the controller 430 can be adapted to manage PLOAM cell addition bydirecting the addition of a PLOAM cell from the PLOAM cell encoder 426to the upstream data path by controlling the cell-type switch 420. Thescrambler 418 scrambles the payload of the input cells and provides themto the overhead insertion module 414 via the burst buffer 416. Theoverhead insertion module 414 associates overhead with each ATM andPLOAM cell, frames the cells and overhead, and provides the upstreamframes to the optical Tx interface 410. The optical Tx interface 410then transmits the upstream frames to the optical module 230 (FIG. 3)for conversion into an optical signal for subsequent transmission over aPON to an OLT. The main components of the upstream data path arediscussed below:

PLOAM Cell Encoder 426

The PLOAM cell encoder 426, in at least one embodiment, is adapted toformat the PLOAM cells and calculate the required check sequences.Particularly, the PLOAM cell encoder 426 is adapted to: format theidentification (IDENT) messages; format the PON ID; format the messagefield; calculate the message field cyclic redundancy check (CRC); formatthe laser control fields; format the receiver control fields; calculatethe Bit Interleaved Parity byte for the PLOAM cell; and the like.

Scrambler Block 418

The scrambler block 418, in one embodiment, is adapted to perform ascrambling operation (as opposed to churning) on the payload of upstreamATM and PLOAM cells received from the cell-type switch 420. In oneembodiment, upstream cells are scrambled using the generatingpolynomial: x⁹+x⁴+1. The generated bit pattern is added modulo 2 to eachupstream cell. The generating polynomial registers (not shown), in oneembodiment, are initialized by the controller 430. The upstream cellshaving scrambled payloads are provided to the overhead insertion module414 via the burst buffer 416.

Upstream Overhead Insertion Module 414

The upstream overhead insertion module 414, in one embodiment, isadapted to retrieve/receive cells from the burst buffer 416 based on theslots granted by the OLT and to affix overhead to each upstream ATM celland/or PLOAM cell received from the burst buffer 416. The overheadcontent is determined by the controller 430 through decoding theupstream_overhead message typically having a guard time, a preamble, anda delimiter programmed by the OLT. The upstream_overhead message can beused by the OLT to adjust the inter-cell gap from different ONT streams,provide a pattern for OLT receiver clock locking, and signal the startof the upstream cell (PLOAM or ATM). The overhead is then inserted intothe outgoing upstream frame as appropriate. In one embodiment, eachupstream frame comprises 53 cell slots to be distributed among the ONTsof a PON, each cell slot representing 56 bytes of data. Either anupstream ATM cell or a PLOAM cell can be added to any given cell slot.In this case, the ATM cells and the PLOAM cells are each 53 bytes inlength (5 bytes of header data, 48 bytes of ATM payload or PLOAM messagedata). The overhead is three bytes in length and is pre-pended to eachATM cell or PLOAM cell to generate an overall data size of 56 bytes,which matches the size of the cell slots of the upstream frame. When anONT has been granted to use a certain cell slot of the upstream frame totransmit a cell, if any, to the OLT, the ONT can provide the upstreamcell the optical module 230 of the ONT 210 (FIG. 2) via the optical Txinterface 41 0 for transmission during the granted slot of the upstreamframe. Additionally, in one embodiment, the overhead insertion module414 is further adapted to adjust the data pattern balance and/or thetransmission equalization delay, as appropriate. Implementations of theoptical Tx interface 410 and the optical Rx interface 404 are discussedwith reference to FIG. 5.

Other Features

Additionally, in at least one embodiment, the APON interface 250includes a general purpose input/output (GPIO) and/or a controlinterface 406 to receive/transmit information between the controller 430and the remainder of the PON processor 240. The control interface 406,in one embodiment, is adapted to provide control information to, andreceive status information from, an optical module to which the APONinterface 250 is connected (e.g., the optical module 230 of FIG. 2).This control information, in one embodiment, includes control data sentto the optical module and/or control information sent to the controller430 of the APON interface 250. In one embodiment, the control interface406 includes, for example, a two wire High Speed I2C interface (perPhillips Version 2.1 1999 specification). With the PON processor 340operating in the master mode, the implementation of a High Speed I2Cinterface typically would allow bit transfer rates of 3.4megabits-per-second (Mbps) across the control interface 406. Addressbits could be implemented to identify the functional or information typeto be accessed. Likewise, data bits could be used to direct a specificaction of the optical module 230 to occur.

Utilizing a 10 bit addressing scheme, adding other required bits (start,acknowledge, etc.), and an 8 bit data scheme generally would allow acontrol word rate of about 147 kilowords per second. This ratecorresponds to about 22 control read/write operations per PON frame.Alternatively, if a 7 bit addressing scheme should be adequate for agiven optical module, the control rate could be increased to 27 controlread/write operations per PON frame. As such, this implementation of thecontrol interface 406 could provide flexibility and adaptability formultiple source optical modules.

The functionality of the optical module 230 controlled via this schemecan include, but is not be limited to: transmitter laser diode bias andmodulation control; transmitter laser diode temperature control (heater,cooler, etc.); receiver trans-impedance amplifier gain or bias control;clock frequency or phase adjustment; test functions such as loop backs,reference or stored data comparisons, self test, etc.; and read statusand alarms such as optics transmitter end of life, environmental, signallevels, etc. These functions, in one embodiment, are controlled oraccessed from the optical module via registers within the opticalmodule. Accordingly, the PON processor 240 can access and adjust theoptical module registers as required by the ONT 21 0 forG.983.X-compliant operation. Although one embodiment of the controlinterface 406 has been illustrated, those skilled in the art may developother implementations of the control interface 406 in accordance withthe present invention using the guidelines provided herein.

In addition to providing improved ease of implementation, theorganization of the APON interface 250, as illustrated, can provide anumber of benefits over discrete implementations of a PON processor. Toillustrate, the use of the deframer module 412 to distinguish ATM cellsand PLOAM cells destined for a specific ONT can significantly reduce theprocessing effort required by other components of the integrated PONprocessor. For example, discrete implementations of a PON processortypically pass all downstream cells to a network protocol processorregardless of their intended destination. As a result, the networkprotocol processor must spend a significant amount of processing effortin determining those cells intended for the ONT and discarding allothers. Likewise, all cells typically are stored in a buffer prior tobeing processed or discarded by the network protocol processor, therebyrequiring a substantial buffer size. However, since the deframer module412 can pre-filter the downstream frames and provide only those ATM andPLOAM cells intended for the corresponding ONT, both the size of theburst buffer 416 and the processing power of the network protocol module320 (FIG. 3) in the integrated PON processor 340 can be reduced comparedto discrete implementations of a PON processor with the samefunctionality.

Similarly, the arrangement of the overhead insertion module 414 inrelation to the burst buffer 416 can reduce the silicon size of the ICand therefore the cost of the IC. Since the overhead insertion module414, in the illustrated embodiment, is adapted to insert the APONoverhead bytes after the data is buffered in the burst buffer 416,upstream and downstream cells stored in the burst buffer 416 are both ofthe same size (e.g., 53 bytes). Accordingly, the ratio of the storage ofthe burst buffer 41 6 assigned to upstream cells to the storage assignedto the downstream cells can be dynamically changed depending on theoperation of the ONT without requiring a complex control mechanism thattypically would be necessary if the upstream and downstream cells storedin the burst buffer 416 were of different sizes. As a result, neither acomplicated control mechanism nor separate burst buffers 416 arenecessary to buffer both upstream and downstream ATM and PLOAM cells.

Referring now to FIG. 5, an exemplary implementation of the opticalinterfaces 404, 410 is illustrated in accordance with at least oneembodiment of the present invention. In at least one embodiment, theoptical interfaces 404, 410 include physical layer interfaces forinterfacing with the optical module 230 (FIG. 2). FIG. 5 illustrates apreferred serial nibble implementations of such physical interfaces,where the optical Rx interface 404 includes a parallel-to-serial (P/S)converter 502 coupled to a serial-to-parallel (S/P) converter 508 of theoptical module 230 and the optical Tx interface 410 includes a S/Pconverter 506 coupled to a P/S converter 504 of the optical module 230.Likewise, the optical module 230 includes a clock 510, a clockmultiplier 512, and a loop back/switch control module 516. The clockrecovery/data module 514 is utilized to extract the clock signal fromthe optical bit stream from the optical module 51 0 (after any clockscaling performed by the clock multiplier 512), clock the data samplesinto and out of the P/S 504 and S/P converters 508, and rate adapt/lockthe optical module clock 510 to the local PON processor clock (notshown). The loop back/switch control module 516, in one embodiment, isadapted to loop back data upstream for troubleshooting or diagnosticpurposes. In at least one embodiment, the optical interfaces 404, 410are adapted to implement Low Voltage Differential Signals capabilitiesbased upon IEEE Standard 1596.3-1996 reduced range implementationcriteria.

For the downstream data, several possible clock multiplier values andthe resulting receive data rate per connection may be used, asillustrated in Table 1. This scheme would not require the ScaleableCoherent Interface signal encoding methods listed in the referencestandard as clock skew would not be an issue at rates up through 1244.16Mbps (Optical Carrier Level 24 or OC24). For the upstream data at 155.52Mbps (asymmetric PON case), two possibilities are shown in the Table 2.Should symmetric rates of 622.08 Mbps or greater be considered, the samescheme as used for the downstream data in Table 1 could be applied forthe upstream data. The overall above listed scheme would also apply forany multiples of Optical Carrier Level 3 (OC3) standard. As such, datarates of 1244.16 Mbps (OC24) or higher could also be easily accommodateduntil the point that clock input and data line skew become an issue withregards to recovered signal fidelity.

TABLE 1 Downstream Data Transmission Rates Aggregate Clock IndividualClock Input Downstream Data Multiplier Connection Data Clock FrequencyRate [Mbps] [N] Rate [Mbps] [MHz] [MHz] 1244.16 8 155.52 19.44 155.52622.08 8 77.76 19.44 77.76 622.08 4 155.52 38.88 155.52 155.52 1 155.5238.88 155.52

TABLE 2 Upstream Data Transmission Rates Aggregate Number of IndividualClock Input Upstream Data Upstream Path Connection Data Frequency Rate[Mbps] Connections Rate [Mbps] [MHz] 155.52 1 155.52 155.52 155.52 277.76 77.76

The illustrated interface scheme of FIG. 5 typically ensuresscalability, ease of implementation, minimal power dissipation, goodcommon mode rejection, low electromagnetic interference (EMI), and allowsimple printed circuit board (PCB) implementation (i.e., less sensitiveto transmission line environment imperfections).

Referring now to FIGS. 6A and 6B, an exemplary implementation of theburst buffer 416 is illustrated in accordance with at least oneembodiment of the present invention. In at least one implementation, theburst buffer 416 serves as a flexible resource for both data paths(upstream and downstream). For example, the burst buffer 416 can be usedto buffer downstream cell bursts and perform upstream cell burstmitigation. To illustrate, assume that downstream data enters the PONprocessor 340 in bursts having a burst transfer rate of 622 Mbps.However, the PON processor 340, in this example, only is able to processdownstream cells at about an Optical Communications Level 3 (OC3) rateof 155 Mbps continuously. As such, the ability to queue up some amountof data until processor bandwidth is available is necessary to preventdata loss. Likewise, upstream data may be provided from the customer tothe PON processor 340 in bursts having a data rate higher than theupstream data transmission rate of the PON. Accordingly, the burstbuffer 416 can be used to buffer the data in the upstream direction toprevent data loss in the upstream direction.

In one embodiment, the burst buffer 416 is implemented as embeddedSDRAM, such as a chip Macro, preferably having a depth of at least about1 megabit. The appropriate depth of the burst buffer 416 is contingentupon the maximum number of consecutive cells in a frame that may beassigned to an ONT. This generally is under the control of the centraloffice OLT and not specified in the ITU G.983.X Recommendation. Theupstream burst depth required is contingent upon the maximum number ofcontiguous cells to be transmitted. The Dynamic Bandwidth Allocation(DBA) standard (i.e., the ITU G.983.4 and G.983.7 Recommendations) onlyspecifies a messaging/control protocol and does not specify thisparameter. It is therefore vendor specific and under the control of theOLT. A depth of at least 1 megabit generally would allow for about 10downstream frames to be buffered in the burst buffer 416 if usedentirely for this purpose (in reality only 1 or 2 frames should berequired under any reasonable bursting scheme). If used for upstreamonly as many as 44 upstream frames could be buffered.

One exemplary mechanism for the burst buffer 416 is described withreference to the illustrated embodiment. The burst buffer 416, in oneembodiment, comprises an upstream buffer portion to buffer upstream dataand a downstream buffer portion to buffer downstream data. Each bufferportion, in one embodiment, comprises a number of memory elements (abit, byte, word, long word, etc.) that can be dynamically and logicallypartitioned into one or more sub-buffers. The size/location of thesub-buffers, in one embodiment, can be modified by, for example, an OLTor the controller 430 (FIG. 4) based on a number of factors, such as apotential for underflow/overflow, a change in the bandwidth associatedwith a particular sub-buffer, the change in the transmissioncharacteristic of a content associated with a particular sub-buffer, andthe like. A transmission characteristic associated with the content caninclude requirements specific to the network protocol used to transmitthe data, the traffic status of the data stream, and the like. Althoughan exemplary implementation of the upstream buffer portion of the burstbuffer 416 is illustrated with reference to FIGS. 6A and 6B, it will beappreciated that the downstream buffer portion of the burst buffer 416can be implemented in a similar manner.

With reference to the illustrated embodiment of FIGS. 6A and 6B, theupstream buffer portion 602 of the burst buffer 416 comprises memoryelements 630-664 partitioned into three sub-buffers 622-626. Eachsub-buffer is associated with a specific data content of the upstreamdata and is specified by a starting and ending address. The sub-bufferentries can be accessed either directly by specifying the logical orphysical address of the entry, or indirectly through a number ofdynamically allocated input and output pointers, including: pointers602, 604 referencing the input and output buffer locations of thesub-buffer 622, respectively; pointers 606, 608 referencing the inputand output buffer locations of the sub-buffer 624, respectively; andpointers 610, 612 referencing the input and output buffer locations ofthe sub-buffer 626, respectively.

The pointers 602-612, in one embodiment, are managed by the controller430. Using their respective input and output pointers, the controller430, in one embodiment, manages the pointers 602-612 to implementsub-buffers 622-626 as circular buffers. As such, each of the pointersis capable of wrapping around its respective sub-buffer when the endaddress of the sub-buffer is reached. Additionally, the controller 430can be adapted to provide the pointers with a flexibleincrement/decrement capability.

For each sub-buffer 622-626, the separation (measured in memoryelements) of its pointer for input indexing and its pointer for outputindexing is referred to as the queue length. The queue length of asub-buffer can be updated automatically by the burst buffer 416 and madeavailable to the controller 430. Based on this queue length information,the controller 430, in one embodiment, is adapted to generate and sendan alarm or appropriate message to be sent to the OLT if the queuelength falls below a minimum threshold or goes above a maximum thresholdset by the PON processor 340 or an OLT.

The ability to signal the OLT regarding the status of the sub-buffers ofthe burst buffer 416, in one embodiment, enables the OLT to implementdynamic bandwidth allocation (DBA) to assign bandwidths to differentcontent transmissions based on the conditions of their associatedsub-buffers and/or the traffic status of their associated data streams.The bandwidth can be allocated between ONTs, between data types, or acombination thereof. To illustrate, assume that a PON is used tosimultaneously transmit video/audio data from a video conference (e.g.,MPEG data), voice content data (e.g., VoIP packets) from a telephonecall, and data traffic (e.g., IP packets) from a content server on theInternet from an OLT to the ONT 210 (FIG. 2). A video conferencetypically requires that a fixed bandwidth with a cell delay/cell delayvariation controlled data pipe be used. Audio telephony generallyrequires that a real time variable bit rate capability (peak cell rate,sustained cell rate, and cell transfer/variation delay) be available.Both of these applications also require that cell loss be minimized. AnInternet data connection often requires a low cell loss ratio but issomewhat flexible as far as delay and bandwidth requirements. Todescribe these transmission characteristics, the ITU G.983.4Recommendation includes a series of five transmission container (T-CONT)types, illustrated in Table 3.

TABLE 3 T-Cont Types T-CONT Type Description 1 Fixed bandwidth, celltransfer delay controlled, cell delay variation controlled 2 Averagerate guaranteed, no delay controlled 3 Assured & non-assured bandwidth,variable rate but not real-time 4 No bandwidth guarantee-best effortonly, no delay control 5 Fixed, assured, non-assured and best effortbandwidth, cell transfer delay controlled, cell delay variationcontrolled

From the T-CONT descriptions of Table 3, it can be determined thatT-Cont type 5 best fits the simultaneous video conference, telephone,and Internet data sessions. The video conference and telephony trafficgenerally would have to fit within the fixed-plus-assured bandwidthservice space. This fixed-plus-assured space could be provisioned suchthat a small amount more than needed is allotted for the connection toallow for some minimal Internet data capability. Additionally, anyexcess not required by the telephony traffic (i.e., since it is variablebit rate some extra may exist) could be applied to Internet traffic. Thenon-assured-plus-best-effort bandwidth would be used for bursty Internetdata conditions such as when downloading a large file.

The burst buffer 416, in this scenario, could place the three upstreamdata contents in logical sub-buffers, with sub-buffer 622 used to bufferupstream data from the telephony session, sub-buffer 624 used to bufferupstream data from the video conference, and the sub-buffer 626 used tobuffer upstream data from the Internet session. These sub-buffers622-624 would make up one T-CONT entity with Type 5 attributes. During afirst time, illustrated with reference to FIG. 6A, the controller 430assigns a queue length of six memory elements to the sub-buffer 622, aqueue length of six memory elements to the sub-buffer 624, and a queuelength of six memory elements to the sub-buffer 626 of the upstreambuffer portion 602.

In this example, assume that amount of upstream data from the telephonysession increases at a second time such that the sub-buffer 624 wouldoverflow unless it is enlarged or the data transmission rate is changed.In one embodiment, the controller 430, noting the rapidly fillingsub-buffer 626, could be adapted to signal the OLT of the status of thesub-buffer 626. Based on this signal, the OLT could be adapted to changethe bandwidth allocation between the three content sessions by assigningmore slot grants to the particular ONT, thereby increasing the upstreamdata transmission rate capability of the ONT. Alternatively, the OLTcould signal the controller 430, using the ITU G.983.4 standard, todynamically modify the queue lengths of one or more of the sub-buffers622-626 to accommodate the increased data rate of the telephony session.

As illustrated in FIG. 6B, since the Internet data session is notreliant on a fixed bandwidth, the queue length of sub-buffer 622associated with the Internet data session can be shortened from sixmemory elements to three memory elements by directing the controller 430to adjust the pointers 602-604. Since the video teleconference session,in this example, is relying on a fixed bandwidth, the queue length ofthe sub-buffer 624 should not be shortened. However, the controller 430can move the logical location of the sub-buffer 624 to make use of someor all of the memory elements freed by the changing of the logicallocation of the sub-buffer 622. The controller 430 can adjust thepointers 606, 608 of the sub-buffer 624 accordingly. By adjusting thequeue length of the sub-buffer 622 and moving the logical location ofthe sub-buffer 624, four memory elements are freed and can beincorporated by the controller 430 to increase the queue length of thesub-buffer 626 by the four freed memory elements by adjusting thepointers 610, 612 to their positions illustrated in FIG. 6B.Accordingly, by utilizing circular sub-buffers and dynamic adjustmentsto the queue lengths of the sub-buffers 622-626, the controller 430 canminimize the potential for buffer overflow/underflow. Likewise, usingthe status of the sub-buffers 622-626 (e.g., the amount of fullness),the controller 430 could monitor fill level, generate required statusreporting messages for use by an OLT, and the like. Similarly, the OLTcan use the status information regarding the buffer portion to performdynamic bandwidth allocation (DBA), determine the operating status ofthe ONT, and the like.

Referring now to FIGS. 7A and 7B, exemplary implementations of thesecurity processor 422 of the APON interface 250 are illustrated inaccordance with at least one embodiment of the present invention. Asnoted above, due to the multicast nature of the PON, downstream cellsgenerally are accessible to all ONUs and ONTs on the network. Withoutfurther protection, PON typically does not provide robust dataprotection. The ITU G.983.1 Recommendation proposes achurning/dechurning system for downstream data protection. Accordingly,in at least one embodiment, the security module 422 includes a dechurnermodule 710 to dechurn the data payloads of received ATM cells inaccordance with the ITU G.983.1 Recommendation. However, there are twobasic weakness of the churning/dechurning system proposed by the ITUG.983.1 Recommendation. First, the proposed key (churning key 714)length is relatively short, being only 24 bits long. Second, thechurning key 714 often is sent publicly by an ONT to an OLT on the PON.The key generally is only protected from other ONTs by the opticalsplitter attenuation and WDM filters.

To enhance the security of the system, the security modules 700A, 700B,in one embodiment, includes a decryption engine 712 to provide truedecryption functionality. The decryption engine 712 can be adapted toimplement any of a variety of encryption/decryption mechanisms, such asDES, 3DES, AES, and RSA to protect the data privacy. The payloads of thecells can be encrypted/decrypted by decryption engines 712 at both endswith the negotiated encryption algorithms. Negotiation of the encryptionalgorithm and the exchange of the keys 716 required for theencryption/decryption algorithms can be performed by protocol exchangesusing vendor specific messages facilitated by the ITU G.983.XRecommendation.

FIG. 7A illustrates an implementation wherein the controller 430provides the dechurner module 710 with a signal indicating whether thedata payloads of the cells being dechurned were encrypted after beingchurned. If the payloads were encrypted, the output of the dechurnermodule 710 is provided to the decryption engine 712, whereupon theencrypted data payloads of the cells is decrypted and the clear ATMcells are provided to the ATM layer of a network protocol stack forfurther processing. Otherwise, the controller 430 directs the dechurnermodule 710 to bypass the decryption engine 712 and provide the ATM cellsdirectly to the ATM layer.

Alternatively, FIG. 7B illustrates an implementation wherein in oneembodiment, the payload of the ATM cells are churned and then encrypted.Accordingly, in this case, the ATM cells from the deframer 412 (FIG. 4)are provided first to the decryption engine 712 of the security module700B, whereupon the payloads are decrypted, and then the ATM cellshaving a decrypted payload are provided to the dechurner 710. Thedechurner 710 dechurns the ATM cells and provides the clear ATM cells tothe ATM layer of a protocol stack (such as implemented by the networkprotocol module 320 of FIG. 3) for processing. In another embodiment,the data payloads of the downstream ATM cells are encrypted but notchurned. Accordingly, in this case, the encrypted downstream ATM cellscan be provided directly to the decryption engine 712 for decryption andsubsequent output as clear ATM cells. Additionally, in at least oneembodiment, the decryption engine 712 can be adapted to encrypt upstreamdata prior to transmission to the OLT.

Referring now to FIG. 8, an exemplary implementation of the controller430 is illustrated in accordance with at least one embodiment of thepresent invention. As noted above, the PON processor 340, in oneembodiment, is implemented as a finite state machine. The configurationof the upstream and downstream data paths, the contents of upstreamtransmission and the timing of the cell transmission are determined bythe state of the system. Events of the finite state machine aregenerated from the controller 430 based in part on received input.Associated with each event input to the finite state machine is acorresponding output of the finite state machine. While, in oneembodiment, state transitions are only initiated as the result ofevents, not all events result in state transitions.

The controller 430, in at least one embodiment, accepts PLOAM cells,timer outputs, physical error signals and fault signals as inputs. Basedon this input and the state of the APON interface 250, the controller430 can generate events as outputs to drive the finite state machine(i.e., the APON interface 250). The controller 430 also can be adaptedto initialize timers for timing events and detectors for the detectionof events. In the illustrated embodiment, the controller 430 comprisessix processing units: a PLOAM cell header processor 810; a PLOAM grantdecoder 820; a PLOAM message decoder 830; an event detector 840; a BIPhandler; and a PLOAM message encoder 860. The outputs of theseprocessing units are events, which trigger the transition of states ofthe finite state machine and produce corresponding actions such asconfiguration of the upstream/downstream data path or responses to OLTrequests.

The functionalities of the processing units of the controller 340 forATM and APON processing are as follows:

PLOAM Cell Header Processor 810

-   1) Verify PLOAM cell header error check (HEC)-   2) Perform frame synchronization-   3) Perform clock recovery (Network Timing Reference)    PLOAM Grant Decoder 820-   1) Decode Grant messages from the OLT-   2) Validate Grant message cyclic redundancy check (CRC)-   3) Set up equalization delay and slot for upstream transmission    PLOAM Message Decoder 830-   1) Identify PLOAM message recipient of received PLOAM message and    discard the message if not relevant.-   2) Verify message CRC, discard the message if the CRC is incorrect,    and generate appropriate response to be sent to OLT for the    indication of error.-   3) Decode the message, generate proper events as the response of the    message.    Detector Module 840-   1) Monitor timer expirations-   2) Perform physical equipment error detection-   3) Perform internal fault detection-   4) Perform signal/pattern detection as required-   5) Determine and monitor the status of the burst buffer 416 for DBA    purposes-   6) Perform OAM functions such as loss of signal (LOS) notification,    OAML, loss of cell delineation (LCD) evaluation, generation of PLOAM    cells, and the like as defined by the ITU G.983.1 Reference.    Bit Interleaved Parity (BIP) Handler 850-   1) Perform BIP calculation for upstream PLOAM cell transmission-   2) Perform Downstream BIP calculation and validation    PLOAM Message Encoder 860-   1) Generate PLOAM messages-   2) Perform CRC calculation

Although the embodiments describer herein have focused on APONapplications, the above description is by way of example only and is nota limitation of the PON processor and system of the present invention,which are applicable in all PON applications and not just APONapplications. Other embodiments, uses, and advantages of the inventionwill be apparent to those skilled in the art from consideration of thespecification and practice of the invention disclosed herein. Thespecification should be considered exemplary only, and the scope of theinvention is accordingly intended to be limited only by the followingclaims and equivalents thereof.

1. In an optical network termination in optical communication with anoptical line termination via a passive optical network and operablycoupled to at least one subscriber device, a burst buffer comprising: anupstream buffer portion configured to buffer upstream data from the atleast one subscriber device; means for providing a representation of astatus of the upstream buffer portion to the optical line terminationfor use in dynamic bandwidth allocation by the optical line termination,wherein the upstream buffer portion includes a plurality of sub-buffers,each sub-buffer being configured to buffer one of a plurality of datacontents of the upstream data, wherein the status of the upstream bufferportion includes a fullness of each of a subset of the sub-buffers; anda control module configured to modify a size of each of the sub-buffersof the upstream buffer portion based at least in part on the fullness ofthe sub-buffer, wherein the control module modifies the size of each ofthe sub-buffers by adjusting a logical location of each sub-buffer suchthat memory elements from one sub-buffer is freed to increase a size ofanother sub-buffer.
 2. The burst buffer as in claim 1, wherein anupstream bandwidth of the passive optical network allocated to theoptical network termination is based at least in part on the status ofthe upstream buffer portion.
 3. The burst buffer as in claim 1, whereinthe status of the upstream buffer portion includes a fullness of theupstream buffer portion.
 4. The burst buffer as in claim 1, wherein aportion of an upstream bandwidth of the passive optical networkallocated to a data content is based at least in part on a transmissioncharacteristic associated with the data content and the fullness of thesub-buffer associated with the data content.
 5. The burst buffer as inclaim 1, further comprising a control module configured to modify a sizeof each of the sub-buffers of the upstream buffer portion based at leastin part on a transmission characteristic of a data stream associatedwith the sub-buffer.
 6. The burst buffer as in claim 1, furthercomprising: a downstream buffer portion configured to buffer downstreamdata from the optical line termination; and means for providing arepresentation of a status of the downstream buffer portion to theoptical line termination for use in dynamic bandwidth allocation by theoptical line termination.
 7. The burst buffer as in claim 6, wherein adownstream bandwidth of the passive optical network allocated to theoptical network termination is based at least in part on the status ofthe downstream buffer portion.
 8. The burst buffer as in claim 6,wherein the status of the downstream buffer portion includes a fullnessof the downstream buffer portion.
 9. The burst buffer as in claim 6,wherein the downstream buffer portion includes a plurality ofsub-buffers, each sub-buffer being configured to buffer one of aplurality of data contents of the downstream data.
 10. The burst bufferas in claim 9, wherein the status of the downstream buffer portionincludes a fullness of each of a subset of the sub-buffers of thedownstream buffer portion.
 11. The burst buffer as in claim 10, whereina portion of a downstream bandwidth of the passive optical networkallocated to a data content is based at least in part on a transmissioncharacteristic associated with the data content and the fullness of thesub-buffer associated with the data content.
 12. The burst buffer as inclaim 10, further comprising a control module configured to modify asize of each of the sub-buffers of the downstream buffer portion basedat least in part on the fullness of the sub-buffer.
 13. The burst bufferas in claim 6, wherein the upstream data includes upstream cells and thedownstream data includes downstream cells, and wherein the upstreamcells and the downstream cells stored in the burst buffer are of a samesize.
 14. The burst buffer as in claim 13, wherein the cells include ATMcells and PLOAM cells.
 15. In an optical network termination in opticalcommunication with an optical line termination via a passive opticalnetwork and in electrical communication with at least one subscriberdevice, a burst buffer comprising: a downstream buffer portionconfigured to buffer downstream data from the optical line termination,wherein the downstream buffer portion includes a plurality ofsub-buffers, each sub-buffer being configured to buffer one of aplurality of data contents of the downstream data; means for providing arepresentation of a status of the downstream buffer portion to theoptical line termination for use in dynamic bandwidth allocation,wherein the status of the downstream buffer portion includes a fullnessof each of a subset of the sub-buffers of the downstream buffer portion;and a control module configured to modify a size of each of thesub-buffers of the downstream buffer portion based at least in part onthe fullness of the sub-buffer, wherein the control module modifies thesize of each of the sub-buffers by adjusting a logical location of eachsub-buffer such that memory elements from one sub-buffer is freed toincrease a size of another sub-buffer.
 16. The burst buffer as in claim15, further comprising: an upstream buffer portion configured to bufferupstream data from the at least one subscriber device; and means forproviding a representation of a status of the upstream buffer portion tothe optical line termination for use in dynamic bandwidth allocation.17. The burst buffer as in claim 15, wherein a downstream bandwidth ofthe passive optical network allocated to the optical network terminationis based at least in part on the status of the downstream bufferportion.
 18. The burst buffer as in claim 15, wherein the status of thedownstream buffer portion includes a fullness of the downstream bufferportion.
 19. The burst buffer as in claim 15, wherein a portion of adownstream bandwidth of the passive optical network allocated to a datacontent is based at least in part on a transmission characteristicassociated with the data content and the fullness of the sub-bufferassociated with the data content.
 20. An optical network termination inoptical communication with an optical line termination and in electricalcommunication with at least one subscriber device, the optical networktermination comprising: a burst buffer including: a downstream bufferportion configured to buffer downstream cells from the optical linetermination; and an upstream buffer portion configured to bufferupstream cells from the at least one subscriber device; and a deframerin electrical communication with the burst buffer and being configuredto: identify a subset of downstream cells from a bitstream transmittedfrom the optical line termination to the optical network termination,the bitstream being representative of downstream data from the opticalline termination; and provide the subset of downstream cells to theburst buffer for buffering; and an overhead insertion module inelectrical communication with the burst buffer and being configured to:extract the upstream cells buffered in the burst buffer; and insertoverhead into each of the extracted upstream cells.
 21. The opticalnetwork termination as in claim 20, further comprising means fortransmitting the extracted upstream cells having inserted overhead tothe optical line termination.
 22. The optical network termination as inclaim 20, wherein the upstream cells buffered in the burst bufferinclude ATM and PLOAM cells and the downstream cells buffered in theburst buffer include ATM cells.
 23. The optical network termination asin claim 20, wherein the each of the upstream cells and the downstreamcells buffered in the burst buffer are of a same size.
 24. The opticalnetwork termination as in claim 20, further comprising a control modulebeing configured to provide a representation of a status of the burstbuffer for transmission to the optical line termination for dynamicbandwidth allocation by the optical line termination.
 25. The opticalnetwork termination as in claim 24, wherein the status of the burstbuffer includes a fullness of the upstream buffer portion.
 26. Theoptical network termination as in claim 25, wherein an upstreambandwidth of the passive optical network allocated to the opticalnetwork termination is based at least in part on the fullness of theupstream buffer portion.
 27. The optical network termination as in claim25, wherein the status of the burst buffer includes a fullness of thedownstream buffer portion.
 28. The optical network termination as inclaim 27, wherein a downstream bandwidth of the passive optical networkallocated to the optical network termination is based at least in parton the fullness of the downstream buffer portion.
 29. A passive opticalnetwork comprising: an optical line termination; at least one subscriberdevice; and at least one optical network termination in opticalcommunication with the optical line termination and operably coupled tothe at least one subscriber device, the optical network terminationincluding: a burst buffer having: an upstream buffer portion configuredto buffer upstream data from the at least one subscriber device; and adownstream buffer portion configured to buffer downstream data from theoptical line termination; and means for providing a representation of astatus of the burst buffer to optical line termination, wherein theoptical line termination is configured to dynamically allocate a portionof a bandwidth of the passive optical network to the optical networktermination based at least in part on the status of the burst buffer,wherein the status of the burst buffer includes a fullness the upstreambuffer portion and downstream buffer portion; and a control moduleconfigured to modify a size of each of the buffer portions based atleast in part on the fullness of the sub-buffer, wherein the controlmodule modifies the size of each of the sub-buffers by adjusting alogical location of each sub-buffer such that memory elements from onesub-buffer is freed to increase a size of another sub-buffer.
 30. Thepassive optical network as in claim 29, wherein the status of the burstbuffer includes a fullness of the upstream buffer portion.
 31. Thepassive optical network as in claim 30, wherein the optical linetermination is configured to dynamically allocate a portion of anupstream bandwidth of the passive optical network to the optical networktermination based at least in part on the fullness of the upstreambuffer portion.
 32. The passive optical network as in claim 30, whereinthe optical line termination is configured to dynamically allocate aportion of an upstream bandwidth of the passive optical network to theoptical network termination based at least in part on a transmissioncharacteristic of the upstream data of the upstream buffer portion. 33.The passive optical network as in claim 30, wherein the upstream bufferportion includes a plurality of sub-buffers, each sub-buffer beingconfigured to store one of a plurality of data contents of the upstreamdata.
 34. The passive optical network as in claim 33, wherein a portionof the upstream bandwidth of the passive optical network allocated toeach of the plurality of data contents is based at least in part on afullness of the sub-buffer associated with the data content.
 35. Thepassive optical network as in claim 29, wherein the status of the burstbuffer includes a fullness of the downstream buffer portion.
 36. Thepassive optical network as in claim 35, wherein the optical linetermination is configured to dynamically allocate a portion of andownstream bandwidth of the passive optical network to the opticalnetwork termination based at least in part on the fullness of thedownstream buffer portion.
 37. The passive optical network as in claim35, wherein the downstream buffer portion includes a plurality ofsub-buffers, each sub-buffer being configured to store one of aplurality of data contents of the downstream data.
 38. The passiveoptical network as in claim 37, wherein a portion of the downstreambandwidth of the passive optical network allocated to each of theplurality of data contents is based at least in part on a fullness ofthe sub-buffer associated with the data content.
 39. The passive opticalnetwork as in claim 29, wherein the status of the burst buffer includesa transmission characteristic of the downstream data of the downstreambuffer portion.
 40. In an optical network termination in opticalcommunication with an optical line termination via a passive opticalnetwork and in electrical communication with at least one subscriberdevice, a method comprising the steps of: storing upstream data from theat least one subscriber device in an upstream buffer portion of a burstbuffer; storing downstream data from the optical line termination in adownstream buffer portion of the burst buffer; providing arepresentation of a status of the burst buffer to the optical linetermination, wherein the status includes a fullness of the upstreambuffer; and modifying a size of the buffers based at least in part onthe fullness of the buffers, wherein the size of the buffers aremodified by dynamically adjusting pointers referencing input and outputbuffer locations of the buffers.
 41. The method as in claim 40, whereina portion of an upstream bandwidth of the passive optical networkallocated to the optical network termination is based at least in parton the fullness of the upstream buffer portion.
 42. The method as inclaim 40, wherein the status includes a fullness of the downstreambuffer portion.
 43. The method as in claim 42, wherein a portion of adownstream bandwidth of the passive optical network allocated to theoptical network termination is based at least in part on the fullness ofthe downstream buffer portion.
 44. In an optical network termination inoptical communication with an optical line termination via a passiveoptical network and in electrical communication with at least onesubscriber device, a computer readable medium comprising a set ofinstructions being configured to manipulate a processor to: storeupstream data from the at least one subscriber device in an upstreambuffer portion of a burst buffer; store downstream data from the opticalline termination in a downstream buffer portion of the burst buffer;provide a representation of a status of the burst buffer to the opticalline termination, wherein the status includes a fullness of the upstreambuffer portion and downstream buffer portion; and modify a size of thebuffers based at least in part on the fullness of the buffers, whereinthe size of the buffers are modified by dynamically adjusting pointersreferencing input and output buffer locations of the buffers.
 45. Thecomputer readable medium as in claim 44, wherein a portion of anupstream bandwidth of the passive optical network allocated to theoptical network termination is based at least in part on the fullness ofthe upstream buffer portion.
 46. The computer readable medium as inclaim 44, wherein a portion of a downstream bandwidth of the passiveoptical network allocated to the optical network termination is based atleast in part on the fullness of the downstream buffer portion.
 47. Inan optical line termination in optical communication with an opticalnetwork termination via a passive optical network, a method comprisingthe steps of: receiving, from the optical network termination, arepresentation of a fullness of an upstream buffer portion of a burstbuffer of the optical network termination, the upstream buffer portionbeing configured to buffer upstream data from at least one subscriberdevice; receiving, from the optical network termination, arepresentation of a fullness of a downstream buffer portion of the burstbuffer, the downstream buffer portion being configured to bufferdownstream data from the optical line termination; allocating a portionof an upstream bandwidth of the passive optical network to the opticalnetwork termination for upstream transmission of the upstream data basedat least in part on the fullness of the upstream buffer portion;allocating a portion of a downstream bandwidth of the passive opticalnetwork to the optical network termination for downstream transmissionof the downstream data based at least in part on the fullness of thedownstream buffer portion; and modifying a size of the buffer portionsbased at least in part on the fullness of the buffer portions, whereinthe size of the buffers are modified by dynamically adjusting pointersreferencing input and output buffer locations of the buffers.
 48. In anoptical line termination in optical communication with an opticalnetwork termination via a passive optical network, a method comprisingthe steps of: receiving, from the optical network termination, arepresentation of a fullness of a first sub-buffer of a burst buffer ofthe optical network termination, the first sub-buffer being associatedwith a first upstream data content of upstream data from at least onesubscriber device; receiving, from the optical network termination, arepresentation of a fullness of a second sub-buffer of the burst buffer,the second sub-buffer being associated with a second data content of theupstream data; allocating a first upstream bandwidth portion to theoptical network termination for upstream transmission of the first datacontent of the upstream data based at least in part on the fullness ofthe first sub-buffer; allocating a second upstream bandwidth portion tothe optical network termination for upstream transmission of the seconddata content of the upstream data based at least in part on the fullnessof the second sub-buffer; and modifying the size of each of thesub-buffers based at least in part on the fullness of the sub-buffers,wherein modifying the size of each of the sub-buffers comprisesadjusting a logical location of each sub-buffer such that memoryelements from one sub-buffer is freed to increase a size of anothersub-buffer.
 49. In an optical line termination in optical communicationwith an optical network termination via a passive optical network, amethod comprising the steps of: receiving, from the optical networktermination, a representation of a fullness of a first sub-buffer of aburst buffer of the optical network termination, the first sub-bufferbeing associated with a first downstream data content of downstream datafrom the optical line termination; receiving, from the optical networktermination, a representation of a fullness of a second sub-buffer ofthe burst buffer, the second sub-buffer being associated with a seconddata content of the downstream data; allocating a first downstreambandwidth portion to the optical network termination for downstreamtransmission of the first data content of the downstream data based atleast in part on the fullness of the first sub-buffer; allocating asecond downstream bandwidth portion to the optical network terminationfor downstream transmission of the second data content of the downstreamdata based at least in part on the fullness of the second sub-buffer;and modifying the size of each of the sub-buffers based at least in parton the fullness of the sub-buffers, wherein modifying the size of eachof the sub-buffers comprises adjusting a logical location of eachsub-buffer such that memory elements from one sub-buffer is freed toincrease a size of another sub-buffer.